The present invention relates to a brake system for automotive vehicles with anti-lock control and traction slip control, including a pedal-actuated braking pressure generator having a master cylinder and a brake power booster, and an auxiliary-pressure supply system which can be switched on during the anti-lock and traction slip control phases and which, on brake application, generates a controlled auxiliary pressure proportional to the pedal force and which, during traction slip control, generates a predetermined, auxiliary pressure limited by the pump output or by a pressure relief valve. The system includes valve assemblies to connect the auxiliary-pressure supply system to the wheel brakes, and outlet valves closed in the inactive position for connecting the wheel brake to a pressure-compensating reservoir in the phase of braking pressure reduction. Wheel sensors and electronic circuitries determine the wheel rotational behavior and generate braking-pressure control signals.
Such a brake system is disclosed in German published patent application No. P 35 27 190.6. In that system a tandem master cylinder and a vacuum power brake booster define a braking pressure generator and an auxiliary-pressure supply system with a hydraulic pump is provided for in whose pressure-fluid circuit from the pressure side to the suction side are inserted in series a braking-pressure control valve and a shut-off valve which is opened in its inactive position. The auxiliary-pressure control valve is controlled by the pressure in one of the working chambers of the master cylinder and, thereby, generates an auxiliary pressure proportional to the pedal force. The shut-off valve, in the form of a two-way/two-position directional control valve that is opened in its inactive position, will be switched over in the traction slip control phase, and will thereby close the pressure-fluid circuit of the pump so that the pressure of the auxiliary-pressure supply system is able to rise until it attains its maximum value. The hydraulic pump is set into operation by an anti-lock or traction slip control signal. During normal, i.e. uncontrolled, braking operations, it will not generate auxiliary pressure. Via valve assemblies, the auxiliary-pressure source in place of the braking pressure generator will be connected to the wheel brakes of the controlled wheels during the control phases. Consequently, the brake system includes only two hydraulically isolated brake circuits, which are static circuits during normal braking operations, into which brake circuits pressure fluid out of the auxiliary-pressure supply system will be introduced dynamically on control action.